1. Field of the Invention
The present invention relates generally to the field of data storage and retrieval, and more particularly to a method for forming a perpendicular magnetic recording head using an air-bearing surface damascene process and perpendicular magnetic recording head formed thereby.
2. Description of Related Art
The first disk drive was introduced in the 1950s and included 50 magnetic disks that were 24-inch in diameter rotating at 1200 RPM (rotations per minute). There has been huge progress in the field of hard disk drive (HDD) technology in almost 50 years since the introduction of the first disk drive. Moreover, the rate of this progress is increasing year after year. Such success has made hard disk storage by far the most important member of the storage hierarchy in modern computers.
The most important customer attributes of disk storage are the cost per megabyte, data rate, and access time. Improvements in areal density have been the chief driving force behind the historic improvement in hard disk storage cost. In fact, the areal density of magnetic disk drives continue to increase, with currently commercially disk drives available with areal densities over 100 billion bits per square inch. While nature allows us to scale down the size of each bit of information, it does not allow scaling to happen forever. Furthermore, while these difficulties have been associated with hard disk drives, similar conclusions would apply to magnetic tape and other magnetic technologies.
A magnetic recording head generally consists of two portions, which include a write portion for storing magnetically encoded information on a magnetic disc and a read portion for retrieving that magnetically encoded information from the disc. The read portion typically consists of a bottom shield, a top shield, and a sensor, often composed of a magnetoresistive (MR) material, positioned between the bottom and top shields. Magnetic flux from the surface of the disc causes rotation of the magnetization vector of a sensing layer of the MR sensor, which in turn causes a change in electrical resistivity of the MR sensor. The change in resistivity of the MR sensor can be detected by passing a current through the MR sensor and measuring a voltage across the MR sensor. External circuitry then converts the voltage information into an appropriate format and manipulates that information as necessary to recover the data that was encoded on the disc.
The write portion of the magnetic recording head typically consists of a top pole and a bottom pole, which are separated from each other at an air bearing surface of the write head by a gap layer, and which are connected to each other at a region distal from the air bearing surface by a back via. Positioned between the top and bottom poles are one or more layers of conductive coils encapsulated by insulating layers. The air bearing surface is the surface of the recording head immediately adjacent the magnetic medium or disc.
To write data to the magnetic medium, an electrical current is caused to flow through the conductive coils, thereby inducing a magnetic field across the write gap between the top and bottom poles. By reversing the polarity of the current through the coils, the polarity of the data written to the magnetic media is also reversed. Because the top pole is generally the trailing pole of the top and bottom poles, the top pole is used to physically write the data to the magnetic media. Accordingly, it is the top pole that defines the track width of the written data. More specifically, the track width is defined by the width of the top pole at the air bearing surface. The write portion and the read portion may be arranged in a merged configuration in which a shared pole serves as both the top shield of the read portion and the bottom pole of the write portion.
As storage capacity demands continue to increase, new serial technologies will gradually replace current parallel SCSI and ATA storage media during the next two years. Beyond these serial advances, hard-disk-drive vendors are working to develop even-more-advanced technologies to improve the physical data recording capacities of HDD magnetic media.
Many HDD manufacturers are beginning to explore a new magnetic recording technology called perpendicular data recording. Perpendicular recording heads for use with magnetic recording media have been proposed to overcome the storage density limitations of longitudinal recording heads.
In today's “longitudinal” HDD products, data bits are recorded on magnetic media using a recording method in which data bits are placed parallel to the media plane. Current longitudinal recording techniques can carry storage densities beyond 100 gigabits per square inch, but new recording methods will be necessary in the coming years to maintain the growth rate in HDD capacity.
To achieve higher storage capacity, drive makers must increase the areal density of the magnetic media. Current methods involve making data bits smaller and placing them closer together, but there are several factors that can limit how small the data bits can be made.
As the data bits get smaller, the magnetic energies holding the bits in place also decrease, and thermal energies can cause demagnetization over time, leading to data loss. This phenomenon is called the super-paramagnetic effect. To counter it, HDD manufacturers can increase the coercivity (the magnetic field required for the drive head to write the data on the magnetic media) of the disk. However, the amount of magnetic field that can be applied is determined by the type of magnetic material used to make the head and the way data bits are written, and vendors are approaching the upper limits in this area.
Perpendicular recording places data bits perpendicular to the magnetic media surface. The data bits are formed in upward or downward magnetic orientation so that transitions will represent 1s and 0s of digital data. Perpendicular recording gives hard drives a much larger areal density in which to store data because it can achieve higher magnetic fields in the recording medium.
Perpendicular recording heads typically include a pair of magnetically coupled poles, with the main pole having a significantly smaller surface area at the air bearing surface than the opposing pole. A coil is located adjacent to the main pole for inducing a magnetic field in the main pole. Magnetic recording media used with perpendicular recording heads typically include a magnetically hard upper layer. A magnetically soft lower layer will typically be located adjacent to the recording layer, opposite the recording head. Due to the difference in surface area between the main pole and opposing pole, and the magnetic flux passing through the soft underlayer between the two poles, the orientation of magnetic flux within the recording tracks will be oriented perpendicular to the recording medium, and parallel to the magnetic flux within the main pole.
The recording density is inversely proportional to the width of the recorded tracks. The width of these tracks is a function of the width of the recording head's main pole. Presently available main poles are currently produced through lithographic processes. The width of the main pole is therefore limited by the resolution of these lithographic processes. In the perpendicular head design with trailing shield, the trailing shield throat height has to be comparable to the gap and track width dimensions. Currently proposed designs for perpendicular heads with “trailing” shields require a “throat height” of less than 100 nm with a tolerance on this of 30 nm or less.
To achieve a “throat height” of less than 100 nm with a tolerance on this of 30 nm or less requires an edge-to-edge alignment between widely spaced layers in the recording head, i.e., the throat height defining layer and the GMR sensor stripe height defining layer that are on the order of 30 nm or less. This requires extremely tight tolerances on alignment and feature sizes during the wafer level process for building the recording head. Semiconductor tooling roadmaps for alignment tolerances suggest that 30 nm dimensions are achievable with leading edge tools, however, no path is currently seen to substantially less than 30 nm. Added to this alignment error are the variation in printed feature size (current semiconductor roadmaps indicate a number around 10 to 30 nm) and any errors in stripe height due to lapping the finished part to define the air bearing surface.
Possible solutions to this edge-to-edge alignment issue include head designs where the stripe height and throat height defining layers are patterned at the same time using a single photo mask. However, this involved a major redesign of the head to something commonly called a side-by-side head, and the process used to build it.
It can be seen then that there is a need for a method and apparatus for providing a perpendicular head that meets decreasing throat height tolerances with more accuracy than provided by photolithography resolutions.